First step to understand the importance of new deep aquifer pumping regime in groundwater system in a developing country, Kwale, Kenya

Nuria Ferrer 1,2, Albert Folch 1,2, Willy Sasaki 3, Mike Lane 3, Calvince Wara 3, Mike Thomas 3, Dan Olago 4, Jacob Katuva 5, Patrick Thomson 5, Emilio Custodio 1 and Rob Hope 5,

1Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya (UPC), Jordi Girona 1-3, 08034 Barcelona, Spain, 2Associated Unit: Hydrogeology Group (UPC-CSIC), 3Rural Focus Ltd., Kenya, 4Department of Geology, University of Nairobi, Kenya, 5Smith School of Enterprise and the Environment, Oxford University, UK

A. INTRODUCTION

Global population growth not only causes increased demand for fresh water, but also provokes a decrease in the quality and quantity of this resource. To avoid this deterioration it is essential to undertake careful management of surface water and groundwater (Pinnuel et al., 2004). Groundwater management starts with an accurate hydrogeological characterization of the aquifer system. This is particularly important in aquifer systems with fast-changing abstraction regimes, as is the case for aquifers in many African countries. In this study of Kwale County, Kenya, we characterize the coastal groundwater system made up of an unconfined shallow aquifer and a confined deep aquifer underlying the shallow.

This groundwater system has long served urban water demands, local communities and an established tourism industry, but now faces unprecedented ground and surface water resource demands, especially from KISCOL (5,500 hectares of irrigated sugarcane) and the country’s largest mining operation (Base Titanium Ltd.) which commenced operations in 2013.

Despite both companies having drilled deep boreholes around the study area (416 km2) to extract groundwater from the deep aquifer, no major pumping activity has started yet, allowing baseline evaluation. Scattered around the study area are 440 handpumps (Thomson et al., 2012) accessing the shallow aquifer to provide drinking water to over 90,000 people.

This work is part of the “Gro for Good: Groundwater Risk for Growth and Development” project, one of a number of consortium projects funded through the UPGro Programme - Unlocking the Potential of Groundwater for the Poor (http://upgro.org/consortium/gro-for-good).

B. OBJECTIVES

The main aim is to define the system and to understand the complex interactions between the aquifer units and water users before major pumping starts. In this presentation we show the results obtained from the first field sampling survey (Sept 2015).

C. METHODOLOGY

Field Parameters

| Field Parameters | Laboratory Analysis | Faecal Bacteria Analysis | |------------------|---------------------|-------------------------| | Ph and Temperature | Cations | DelAgua Kit | | pH and T | Ca | pH | pH | | Electrical Conductivity | Anions | DelAgua Kit | | EC | Cl | pH | pH | | Alkalinity | Trace Elements | DelAgua Kit | | Digital meter by SARTA of the USA | ICP-AES | DelAgua Kit |

D. RESULTS AND DISCUSSION

The isotopic signal is lighter at higher altitudes such as Shimba Hills Range (west area). Similar signals are found in the samples from the deep boreholes located on the coastal area.

E. CONCLUSIONS

- The initial field survey and analysis has provided a useful start towards understanding the recharge area and zone for the deep aquifer and characterizing the groundwater quality of both deep and shallow aquifer systems.
- Improved knowledge of the deep aquifer system will be very important for sustainable water management in the Kwale area as water demands are placed on this resource.
- Isotopic signals suggest that the recharge area of the deep aquifer is located on the west part of the study area, on the Shimba Hills Range, and that the recharge of the aquifer is quite fast.
- As so many people depend on the shallow aquifer for their drinking water, monitoring water quality in this aquifer is also important for management. TTF pollution is indicated in many open wells, although the source is not yet defined (see Future research).
- The scale project will be gathering more evidence relating to the impacts that improved water supplies can have on communities.
- The industrial sugar cane plantations do not appear to be a source of nitrate pollution.

F. FUTURE RESEARCH

- Study the hydrochemical evolution of the system comparing dry (March) and wet (June) seasons.
- Define the connection between aquifer units.
- Create a groundwater flow model of the system.
- Define the sources and mechanisms of chemical and biological contamination.

G. REFERENCES

Pinnuel, H., Binger, R., Filippini, D., Serrano, M., Wold, H., Kandiah, E., et al. Water resources and agricultural use in semi-arid areas. Water Resources Management 18, 395-414 (2004). Levin, N.E., Zipser, E.J., Ceding, T.E., 2009. Isotopic composition of waters from Ethiopia and Kenya. Hydrogeology Journal 17, 1141-1151. Thomson, P., Hope, R., Parry, T., 2012. GIS model source monitoring of rural handpumps: a pilot study of rural handpumps in 140 villages in Kenya. Hydrogeology Journal 20, 269-280.

Hydrochemical results:

- Calcium bicarbonate facies are predominated.
- Most of the wells which present saline intrusion are located on the coastal area, on Pleistocene coastal geological materials.
- There is a clear correlation between rift diagrams and geological units.
- The residence time is low.